1. Field of the Invention
The present invention relates to a piezoelectric vibrating piece, a piezoelectric vibrator, an oscillator, an electronic device, and a radio-controlled timepiece.
2. Description of the Related Art
For example, in a mobile phone and a personal digital assistant, it is often the case that a piezoelectric vibrator which makes use of crystal or the like is used as a time source, a timing source for control signals, a reference signal source or the like. As this kind of piezoelectric vibrator, there has been known a piezoelectric vibrator where a tuning-fork-type piezoelectric vibrating piece is hermetically sealed in a package where a cavity is formed.
The package has the structure where a pair of glass substrates (ceramic substrates also being used) in which a recessed portion is formed on one of the glass substrates is overlapped to each other and is directly bonded to each other thus providing the structure where the recessed portion functions as a cavity. Further, the piezoelectric vibrating piece includes a pair of vibrating arm portions which is arranged parallel to each other, and a base portion to which longitudinal proximal end sides of both vibrating arm portions are integrally fixed. Both vibrating arm portions of the piezoelectric vibrating piece vibrate (swing) in the direction that the vibrating arm portions approach each other or are separated from each other with predetermined resonance frequency using proximal end sides thereof as starting points.
Recently, as represented by a mobile phone or the like, the miniaturization of various electronic devices each of which incorporates a piezoelectric vibrator therein has been in progress. Accordingly, there has been a demand for further miniaturization with respect to a piezoelectric vibrating piece which constitutes the piezoelectric vibrator. In view of such circumstances, studies have been made to shorten a total length of the piezoelectric vibrating piece by shortening a base portion of the piezoelectric vibrating piece, for example.
However, in mounting the piezoelectric vibrating piece, the piezoelectric vibrating piece is mounted by way of a base portion and hence, when a length of the base portion is shortened, there arises a drawback that a mounting performance is deteriorated. Accordingly, the length of the base portion is usually designed to be as short as possible within a range where the mounting performance can be ensured.
It has been also known that the vibration leakage (leakage of vibration energy) is generated via a base portion of a piezoelectric vibrating piece when the piezoelectric vibrating piece is operated. This vibration leakage is linked with the rise of a CI value (Crystal Impedance) and hence, it is necessary to suppress the vibration leakage as much as possible. In this respect, the vibrations of a vibrating arm portion can be stabilized by setting a length of the base portion as large as possible so that the vibration leakage can be efficiently suppressed. However, as described above, from a viewpoint of miniaturization, the length of the base portion is designed to be as short as possible within a range where the mounting performance can be ensured and hence, there has been a demand for the constitution which can suppress the vibration leakage without changing the length of the base portion.
In view of the above, JP-A-2002-261558 (patent literature 1) discloses the constitution where cutaway portions (notches) which are formed by cutting a base portion toward the center in the widthwise direction from both sides of the base portion are formed between the connecting portion of the base portion where the base portion is connected to the vibrating arm portion and the mount portion thus forming a portion of the base portion where the cutaway portions are formed as a narrow width portion where a width is narrow compared to other portions of the base portion.
Due to such a constitution, the vibrations excited by a vibrating arm portion can be confined in a vibrating arm portion side whereby the leakage of vibrations toward the base portion side can be suppressed.